Catalytic systems and process for treatment of industrial process and waste streams

ABSTRACT

A process for preparing supported catalyst in pellet or coated monolith form is disclosed the method includes the steps of: forming a mixed metal carbonate complex having at least two metals by subjecting a first metal carbonate containing compound to ion exchange with desired metal cations; heat treating the resulting mixed metal carbonate complex to form a mixed oxide which consists of active metal oxides supported on a catalyst support; forming the resulting supported catalysts into pellets or coating the resulting supported catalyst onto a monolithic support. The catalysts may be used for treating effluents containing organic material in the presence of an oxidising agent.

FIELD OF INVENTION

This invention relates to catalytic systems and a catalytic process forwet oxidation of organic-containing industrial process and wastestreams.

BACKGROUND OF INVENTION

The removal of organic substances from process and waste streams poses asignificant challenge for many industries. This challenge has furtherbeen compounded by the increasing rigorous quality control restrictionsimposed on manufacturing industries. Depending on the nature of theindustry, organic substances in industrial process and waste streams canbe a complex mixture of different compounds ranging from simple lowmolecular weight hydrocarbons such as alcohols, aldehydes, ketones,carboxylic acids, low molecular weight fatty acids to high molecularweight hydrocarbons such as fulvic and humic acids. Organic substancesin industrial waste effluents may contain nitrogen, chloride, and sulfurand some effluents contain process chemicals which need to be recycled,e.g. black liquor from Bayer process and pulp mill.

Conventional methods for the treatment of organic-containing industrialeffluents include biological and physical treatments, incineration andwet air oxidation. Biological treatment is the most widely used methoddue to its simplicity and low cost. However, the microorganisms used forthis process are effective for only low organic content wastes. Thus forhigh organic content wastes, methods such as wet air oxidation becomevery attractive.

It is known from the prior art that wet air oxidation is a process inwhich organic substances in aqueous streams are oxidised by an oxidant.Depending on reaction conditions and the type of organic compound to beoxidised, both non-catalytic and catalytic wet oxidation can be used toconvert organic substances into CO₂ and biodegradable low molecularsubstances, such as mono or dicarboxylic acids.

Non catalytic wet air oxidation is a well-established technique forwaste water treatment (Swed. Pat. 34941,1911). It entails the liquidphase oxidation of organics and oxidisable inorganics at elevatedtemperatures (up to 320° C.) and pressures (up to 20 MPa) using agaseous source of oxygen. The extreme conditions employed often resultin severe technical difficulties as well as increased capital cost.

Catalytic wet oxidation is a promising alternative technique, which canoperate at lower temperatures and pressures. Catalytic wet oxidation canbe carried out by means of homogeneous or heterogeneous catalysis. Thereare a number of homogeneous catalytic systems reported which effectivelyoxidise organic substances from aqueous streams. Examples of suchcatalytic systems are CuSO₄ and Cu(NO₃)₂. (Lei et al., Wat. Sci. Tech.,Vol. 35, No. 4, 1997, pp 311-319; Lin and Ho, J. Environ. Eng.,September, 1997, pp 852-858). However, the need for down streamprocessing to remove the spent catalyst is a distinct disadvantagemaking homogeneous technology commercially infeasible.

Heterogeneous catalysis appears to be a better alternative. Inheterogeneous oxidation catalysis, the catalytic activity isattributable to surface oxygen available on the solid catalyst. A goodcatalyst is characterised by high surface oxygen availability and fastoxygen transfer ability. Depending on the application, the catalyst maybe in the form of a powder, pellets or a monolith.

Traditionally, catalytic wet air oxidation is carried out in slurry ortrickle bed reactors. In slurry reactors, the catalyst has to berecycled continuously to the reactor. Unfortunately, separation of thefine catalyst particles can be troublesome, costly and time-consuming.To overcome this, a trickle bed reactor with catalyst in the form ofpellets or monoliths may be used. Catalysts in the form of pellets arewell known as are techniques for forming such pellets. In the monolithicsystem, catalytic materials are deposited onto the monolith support inthe form of a very thin layer. The monolith support can be in the formof honeycombs with parallel open channels. Reactants may flow throughthe monolithic channels. In this reactor configuration, the need tofilter and recycle catalyst back to the reactor is eliminated.

Industrial interest has stimulated numerous investigations intocatalysts for wet oxidation of organic substances from process and wastestreams. Although a number of catalytic systems have been reported inthe open and patent literatures, most of the catalytic systems requiresevere conditions, namely high pressures and high temperatures, in orderto achieve significant oxidation rate (U.S. Pat. No. 4,268,399-A; Eur.Pat. 90313238.9; Lin and Ho, J. Environ. Eng., September, 1997, pp852-858; Zhang and Chuang, Ind. Eng. Chem. Res., 37, 1998, pp3343-3349). In some catalytic systems, strong oxidants such as ozone andH₂O₂ are required (Centi et al., Catal. Today, 55, 2000, pp 61-69;Gulyas et al., Wat. Sci. Tech., Vol 32, No 7, 1995, pp 127-134).

Accordingly, it is an object of the present invention to overcome, or atleast alleviate, the difficulties presented by prior art.

SUMMARY OF INVENTION

In a first aspect, the present invention provides a process forpreparing a supported catalyst in pellet form or coated monolith formwhich process includes:

forming a mixed metal carbonate complex having at least two metals bysubjecting a first metal carbonate containing compound to ion exchangewith desired metal cations;

heat treating the resulting mixed metal carbonate complex to form amixed oxide which consists of active metal oxides supported on acatalyst support;

forming the resulting supported catalysts into pellets or coating theresulting supported catalyst onto a monolithic support.

Preferably the first metal carbonate containing compound is ammoniumdawsonite NH₄Al(OH)₂CO₃ and this includes hydrates of such compounds.However, other metal carbonates, including sodium dawsonite,NaAl(OH)₂CO₃ may also be used.

Active metal oxides are preferably selected from Co, Mn, Cu, Ni, Pt, Zn,Fe, Cr, V, Ru, Rh, Pd, Pt, Ag and Ce. More preferred metal oxides arereducible metals selected from the transition metal groups. Preferablythey are present in the range of 0.5 to 20 wt % of the supportedcatalyst.

The active metal oxides may be present in any oxidation state. They maybe chemically bound to the support surface or may be present as separatecrystalline phases.

The supported catalyst may contain one or more additional components,which alter its activity and selectivity. These additional componentsmay be selected metals of the groups IA and IIA, lanthanides, sulphidesand mixtures thereof.

The ammonium dawsonite may be prepared by reacting a solution containinga soluble salt of aluminium such as the sulfate or nitrate with asolution of ammonium bicarbonate with or without aqueous ammonia.However, the metal carbonate may be obtained from natural as well asother synthetic routes.

The monolithic support may be obtained commercially or may be fabricatedfrom any material such as cordierite (magnesium aluminium silicate),alumina, silica-alumina, red mud, or the like.

The present invention also provides a process for preparing a supportedmetal catalyst precursor by exchanging at least two different reduciblemetal ions with a metal carbonate-containing compound such as adawsonite or a dawsonite like compounds, for example NH₄Al(OH)₂CO₃.

The metal carbonate containing compound may be obtained from anysuitable sources, such as a mineral ore or a synthetic compound. In thisaspect, the metal carbonate containing compound functions as a catalystsupport precursor. Subsequent heat treatment decomposes the system intothe supported catalyst.

The invention also provides a method of preparing catalysts comprisingthe steps of:

-   -   preparing ammonium dawsonite    -   adding solutions containing ions of at least one catalytically        active component selected from the group consisting of Co, Mn,        Cu, Ni, Pt, Zn, Fe, Cr, V, Ru, Ag and Ce to the ammonium        dawsonite.    -   allowing ion exchange to take place    -   separating the solid from the solution    -   washing and drying the solid    -   heating the solid to a temperature high enough to form supported        catalysts.

The invention also provides a method of producing supported monolithiccatalysts comprising the steps of:

-   -   forming a slurry of the catalyst and wash-coating it on the        monolithic support    -   drying the wash-coated monolithic support    -   heating the wash-coated monolithic support to a temperature high        enough to activate it.

Supported monolithic catalysts may also be produced by wash-coating ametal carbonate complex such as ammonium dawsonite, NH₄Al(OH)₂CO₃, ontothe monolith support followed by an ion exchange step with desiredcations. This process may comprise of the following steps:

-   -   forming a mixed metal carbonate complex    -   forming a slurry of the mixed metal carbonate and wash-coating        it on the monolith support    -   exchanging with desired cations    -   drying the wash-coated monolith    -   heating the wash-coated monolith to a temperature high enough to        activate the catalyst

According to a further aspect of the invention, there is provided aprocess for the treatment of effluents obtained from industries such aspulp and paper, textile etc. This involves contacting the effluent withthe catalyst of the present invention in the presence of an oxidisingagent.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be further described by reference topreferred embodiments described in the following examples. It musthowever be noted that, the details thereof do not represent a limitationof the invention.

EXAMPLE 1

This example describes the preparation of an ammonium dawsonite support.

A 360 ml solution containing 22 g Al₂SO₄.18H₂O was added drop-wise to a180 ml alkaline solution containing 20 g NH₄HCO₃ and 31.6 g aqueous NH₃(25%) while stirring was in progress. The resulting precipitate was agedfor 15 hours, washed with water and dried in air. This material had thecomposition NH₄Al(OH)₂CO₃ with 36% Al₂O₃ on calcination and wasdesignated SUPPORT I.

EXAMPLE 2

This example describes the preparation of an ammonium dawsonite support.

A 300 ml solution containing 23.9 g Al₂SO₄.18H₂O was added drop-wise toa 150 ml alkaline solution containing 22.7 g NH₄HCO₃ while stirring wasin progress. The resulting precipitate was washed with water and driedin air. This material had the composition NH₄Al(OH)₂CO₃ which also gave36% Al₂O₃ on calcination and was designated SUPPORT II.

EXAMPLE 3

This example describes the preparation of a catalyst having 0.4 wt %Fe₂O₃, 0.9 wt % CuO and 7.9 wt % Co₂O₃ supported on alumina.

A 20 ml solution containing 1.78 g Co(NO₃)₂.6H₂O, 0.18 g Cu(NO₃)₂.₃H₂Oand 0.15 g Fe(NO₃)₃.9H₂O was added drop-wise to a 60 ml slurrycontaining 16 g of SUPPORT I (36 wt. % Al₂O₃) from Example 1 whilestirring was in progress. After adding the above solution, stirring wascontinued for about 4 hours. The solid was then separated bycentrifugation, washed with water, dried in air overnight and calcinedat 300° C. for 4 hours to give the desired catalyst composition.

EXAMPLE 4

This example describes the preparation of a catalyst having 4.9 wt %Fe₂O₃, 4.5 wt % Mn₂O₃ and 3.3 wt % CaO supported on alumina.

A 20 ml solution containing 0.9 g Fe(NO₃)₃.9H₂O, 0.34 g Ca(NO₃)₂, and0.36 g Mn(NO₃)₂ was added drop-wise to a 40 ml slurry containing 8.6 gof the ammonium dawsonite SUPPORT II (36 wt. % Al₂O₃) from Example 2while stirring was in progress. After adding the solution, stirring wascontinued for 4 hours. The solid was then separated by filtration,washed with water, dried in air overnight and calcined at 400° C. for 4hours to give the desired catalyst composition.

EXAMPLE 5

This example describes the preparation of a catalyst having 2.5 wt %Co₂O₃, 7.4 wt % Mn₂O₃ and 2.2 wt % BaO supported on alumina.

A 20 ml solution containing 0.32 g Co(NO₃)₂.6H₂O, 0.6 g Mn(NO₃)₂ and0.136 g Ba(NO₃)₂ was added drop-wise to a 40 ml slurry containing 8.6 gof the ammonium dawsonite SUPPORT I (36 wt % Al₂O₃) prepared inexample 1. After about 4 hours of stirring, the solid was separated bycentrifugation, washed with water, dried in air overnight and calcinedat 300° C. for 4 hours to give the desired catalyst composition.

EXAMPLE 6

This example describes the preparation of a catalyst having 6.7 wt %Co₂O₃ and 3.7 wt % Mn₂O₃ supported on alumina.

A 10 ml solution containing 0.16 g Mn(NO₃)₂ and 0.43 g Co(NO₃)₂.6H₂O wasadded drop-wise to a 20 ml slurry containing 4.60 g of the ammoniumdawsonite SUPPORT II (36 wt % Al₂O₃) prepared in Example 2 whilestirring was in progress. After about 4 hours of stirring, the solid wasseparated by centrifugation, washed with water. The solid was separatedby centrifugation, dried in air overnight and calcined at 250° C. for 4hours to give the desired catalyst composition. The catalyst had asurface area of 170 m2/g.

EXAMPLE 7

This example describes the preparation of a catalyst having 9 wt % CuOsupported on alumina.

The procedure of Example 5 was followed, except that a 20 ml solutioncontaining 0.91 g Cu(NO₃)₂.3H₂O was used to give the desired catalystcomposition.

EXAMPLE 8

This example describes the preparation of a catalyst having 7.2 wt %Co₂O₃ and 1.8 wt % Cr₂O₃ supported on alumina.

The procedure of Example 5 was followed, except that a 20 ml solutioncontaining 0.84 g Co(NO₃)₂ and 0.32 g Cr(NO₃)₂.9H₂O was used.

EXAMPLE 9

This example describes the preparation of a catalyst having 6.6 wt %CO₂O₃, 2.5 wt % CuO, 1.2 wt % CeO₂ and 0.2 wt % Ag₂O supported oncordierite monolith.

A 400 ml solution containing 1.34 g AgNO₃, 86.06 g Co(NO₃)₂.6H₂O, 28.18g Cu(NO₃)₂.3H₂O and 14.90 g (NH₄)₂Ce(NO₃)₆ was added drop-wise to a 1000ml alkaline solution containing 70 g of Na₂CO₃ while stirring was inprogress. The resulting precipitate was washed with water, dried in airovernight and calcined at 250° C. for 4 hours.

100 ml of H₂O was added to 10 g of the mixed metal oxide prepared aboveand milled for about 20 minutes to obtain a smooth slurry. Commerciallyobtained cordierite monolith was cut into cylindrical blocks each havinga diameter of 15 mm and height of 25 mm. These blocks were immersed (oneat a time) in the mixed metal oxide slurry while stirring was inprogress until all the channels were coated. The coated block was thendried in air overnight. The coating process was repeated 3 times. Afterthe third coating, the monolith was dried in air overnight and calcinedat 300° C. for 4 hours.

EXAMPLE 10

This example describes the preparation of a catalyst having 3.0 wt %Co₂O₃, 2.4 wt % CuO, 3.0% wt % Fe₂O₃, 1.2 wt % CeO₂, 0.4 wt % Ag₂Osupported on alumina.

A 90 ml solution containing 2.17 g Co(NO₃)₂.6H₂O, 1.46 g Cu(NO₃)₂.₃H₂O,3.13 g Fe(NO₃)₃.9H₂O, 0.76 g (NH₄)₂Ce(NO₃)6 and 0.13 g AgNO₃ was addeddropwise to a 180 ml slurry containing 48.65 g of the ammonium dawsoniteSUPPORT II (36 wt. % Al₂O₃) prepared in Example 2 while stirring was inprogress. After about 2 hours of stirring, the solid was separated bycentrifugation, washed with water, dried in air overnight and calcinedat 300° C. for 4 hours to give the desired catalyst composition.

EXAMPLE 11

The method used in example 9 was followed except that the catalystprepared in Example 10 was wash coated onto a commercial monolith.

EXAMPLE 12

This example describes the treatment of pulp and paper effluent using acatalyst according to the present invention.

1.4 g of catalyst prepared in accordance to Example 7 was added to 70 mlof effluent obtained from the pulp and paper industry. The catalyst andeffluent were allowed to react in an autoclave at 90° C. for 2 hours inthe presence of 800 kPa gaseous air. A reduction in colour of 86% wasachieved.

EXAMPLE 13

This example describes the treatment of pulp and paper effluent using acatalyst according to the present invention.

2 g of catalyst prepared in accordance to example 6 was added to 100 mlof effluent obtained from the pulp and paper industry. The catalyst andeffluent were allowed to react in an autoclave at 70° C. for 2 hours inthe presence of 800 kPa gaseous air. A reduction in colour of 87% wasachieved.

EXAMPLE 14

This example describes the treatment of pulp and paper effluent using acatalyst according to the present invention.

2 g of catalyst prepared in accordance to example 6 was added to 100 mlof effluent obtained from the pulp and paper industry. The catalyst andeffluent were allowed to react in an autoclave at 90° C. for 2 hours inthe presence of 800 kPa gaseous air. A colour removal of 90% and CODreduction of 80% were achieved.

EXAMPLE 15

This example illustrates the fact that the catalyst may be reused andalso regenerated.

The spent catalyst from Example 14 was recovered and added to 100 ml offresh effluent obtained from the pulp and paper industry. The spentcatalyst and fresh effluent were allowed to react under the sameconditions used in example 14. This procedure was repeated 6 times.After 6 runs, the catalyst activity was decreased by 15%. Full catalystactivity can be restored by heating the spent catalyst in air at 300° C.for 4 h.

EXAMPLE 16

This example describes the treatment of textile effluent using acatalyst according to the present invention.

1 g of catalyst prepared in accordance to Example 8 was added to 100 mlof waste effluent obtained from the textile industry. The catalyst andeffluent were allowed to react in an autoclave at 70° C. for 1 hour inthe presence of 400 kPa gaseous air. A reduction in colour of 91% wasachieved.

EXAMPLE 17

This example illustrates the treatment of textile effluent using acatalyst according to the present invention.

1.4 g of catalyst prepared in accordance to example 3 was added to 70 mlof waste effluent obtained from the textile industry. The catalyst andeffluent were allowed to react in an autoclave at 90° C. for 4 hour inthe presence of 800 kPa gaseous air. A reduction in COD of 86% wasachieved.

EXAMPLE 18

This example illustrates the treatment of pulp and paper effluent usinga catalyst according to the present invention.

A flow of effluent (1 ml/min) obtained from pulp and paper industry(COD=2500 ppm, colour=2000 HU) and a flow of air (20 ml/min) wereallowed to react in an 80 ml tubular reactor packed with 12 blocks ofthe catalyst prepared in accordance to example 9. At a reactortemperature of 90° C., COD and colour reduction of 63% and 90%respectively were achieved.

EXAMPLE 19

This example illustrates the deodorisation of pulping process liquorusing a catalyst according to the present invention.

80 ml of pulping process liquor was put in a glass bubbler, which wassubmerged in the water bath at 90° C. An air flow was bubbled throughthe liquor at a flow rate of 13 ml/min. The volatile componentsvaporised at 90° C. carried over with air was flowed over an 80 mltubular reactor packed with 12 blocks of catalyst prepared in accordanceto example 11. At a reactor temperature of 95° C., the following resultswere obtained. % removal Substance treated (run time = 4 hours) H₂S >99Methyl mercaptan >99 Ethyl mercaptan >99 Dimethyl sulfide >99 Dimethyldisulfide >95 Dimethyl trisulfide >99

EXAMPLE 20

This example illustrates the treatment of petrochemical effluent using acatalyst according to the present invention.

1 ml/min of effluent obtained from the petrochemical industry (COD=1520ppm) and 100 ml/min of air were allowed to react in an 80 ml reactorpacked with 12 blocks of the catalyst prepared in accordance to example9. At a reactor temperature of 90 C., a reduction in COD of 74% wereachieved.

Since modification within the spirit and scope of the invention may bereadily effected by persons skilled in the art, it is to be understoodthat the invention is not limited to the particular embodimentdescribed, by way of example, hereinabove.

1. A process for preparing a supported catalyst in pellet form or coatedmonolith form which includes: forming a mixed metal carbonate complexhaving at least two metals by subjecting a first metal carbonatecontaining compound to ion exchange with desired metal cations; heattreating the resulting mixed metal carbonate complex to form a mixedoxide which consists of active metal oxides supported on a catalystsupport; forming the resulting supported catalysts into pellets orcoating the resulting supported catalyst onto a monolithic support.
 2. Aprocess as defined in claim 1 wherein the first metal carbonatecontaining a compound is ammonium dawsonite, NH₄Al(OH₂)CO₃.
 3. A processas defined in claim 1 or claim 2 wherein the desired metal cations arederived from the group of metals consisting of Co, Mn, Cu, Ni, Pt, Zn,Fe, Cr, V, R, Rh, Pd, Pt, Ag and Ce.
 4. A process as defined in claim 3wherein the metals are transition metals.
 5. A process as defined in anyone of claims 1 to 4 wherein the active metal oxides are present in therange of 0.5 to 20 wt % of the supported catalyst.
 6. A process asdefined in any one of claims 1 to 5 wherein the supported catalystfurther contains metals of Groups IA, IIA and lanthanides.
 7. A processas defined in any one of claims 1 to 6 wherein the monolithic supportmay be obtained commercially or may be fabricated from cordierite(magnesium aluminium silicate), alumina, silica-alumina, red mud, or thelike.
 8. A process for obtaining a supported metal catalyst precursor byexchanging at least two different reducible metal ions with a metalcarbonate-containing compound such as a dawsonite or a dawsonite likecompound.
 9. A method of preparing catalysts comprising the steps of:preparing ammonium dawsonite adding solutions containing ions of atleast one catalytically active component selected from the groupconsisting of Co, Mn, Cu, Ni, Pt, Zn, Fe, Cr, V, Ru, Ag and Ce to theammonium dawsonite. allowing ion exchange to take place separating thesolid from the solution washing and drying the solid heating the solidto a temperature high enough to form supported catalysts.
 10. A methodof producing supported monolithic catalysts comprising the steps of:forming a slurry of the catalyst and wash-coating it on the monolithicsupport drying the wash-coated monolithic support heating thewash-coated monolithic support to a temperature high enough to activateit.
 11. A method of preparing supported monolithic catalysts bywash-coating a metal carbonate complex onto a monolith support followedby an ion exchange step with desired cations, wherein the processcomprises the following steps: forming a mixed metal carbonate complexforming a slurry of the mixed metal carbonate and wash-coating it on themonolith support exchanging with desired cations drying the wash-coatedmonolith heating the wash-coated monolith to a temperature high enoughto activate the catalyst
 12. A supported catalyst prepared by a processas defined in any one of claims 1 to
 11. 13. A method of treatment ofeffluents containing organic material obtained from industries includingpulp and paper, textile, and the like, the method comprising contactingthe effluent with the catalyst as defined in claim 12 in the presence ofan oxidising agent.